Composite positive electrode active material for lithium secondary battery and method for preparing same

Abstract

The present invention relates to a composite positive electrode active material for a lithium secondary battery and a method for preparing the same. The composite positive electrode active material may include: a core part capable of intercalating and deintercalating lithium; and a shell part covering the surface of the core part and including an alkali metal oxide, in which the alkali metal oxide may include a substitution element that substitutes a part of an alkali metal element and has a higher oxidation number than the alkali metal element.

Description

Technical Field

[0001] The invention relates to a composite positive electrode active material for a lithium secondary battery and a preparation method thereof. Background Art

[0002] Secondary batteries that can be charged and discharged are used not only in small electronic devices such as mobile phones and laptops, but also in large transportation vehicles such as hybrid cars and electric cars. Therefore, it is necessary to develop a secondary battery with higher stability and energy density.

[0003] Most of the existing secondary batteries are based on organic liquid electrolytes, and therefore have limitations in improving stability and energy density.

[0004] In addition, all-solid-state batteries using inorganic solid electrolytes are based on technology that eliminates organic solvents, allowing batteries to be manufactured in a safe and simple form, and have therefore attracted attention in recent years.

[0005] However, all-solid-state batteries have problems such as high interfacial resistance at the interface between the positive electrode active material and the solid electrolyte and side reactions. Therefore, although the side reactions are mitigated by applying a coating containing an oxide-based compound to the positive electrode active material, the coating is decomposed when the all-solid-state battery is operated for a long time. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] The object of the present invention is to provide a composite positive electrode active material for lithium secondary batteries and a preparation method thereof, which can reduce the high interface resistance between the positive electrode active material and the solid electrolyte.

[0008] The object of the present invention is to provide a composite positive electrode active material for lithium secondary batteries having high chemical adsorption strength and chemical stability and a preparation method thereof.

[0009] The object of the present invention is to provide a composite positive electrode active material for lithium secondary batteries with excellent lithium ion conductivity and a preparation method thereof.

[0010] The object of the present invention is not limited to the above-mentioned object. The object of the present invention will become more clear through the following description, and can be achieved through the methods and combinations described in the claims.

[0011] (II) Technical solution

[0012] A composite positive active material for a lithium secondary battery according to an embodiment of the present invention may include: a core portion capable of inserting and extracting lithium; and a shell portion covering a surface of the core portion and including an alkali metal oxide.

[0013] The alkali metal oxide may include a substituent element which replaces a part of the alkali metal element and has an oxidation number higher than that of the alkali metal element.

[0014] The substituting element may comprise a non-transition metal.

[0015] The alkali metal oxide may be represented by Chemical Formula 1 below.

[0016] [Chemical formula 1]

[0017] (A 1-ax B x )MO 3

[0018] In the chemical formula 1, the A may include an alkali metal element, the B may include at least one selected from magnesium (Mg), aluminum (Al), gallium (Ga), silicon (Si), germanium (Ge), tin (Sn), arsenic (As), antimony (Sb), and combinations thereof, the M may include at least one selected from niobium (Nb), tantalum (Ta), boron (B), zirconium (Zr), phosphorus (P), and combinations thereof, the a may be an oxidation number of the B, and may satisfy 0.01≤x≤0.3.

[0019] The alkali metal oxide may be represented by Chemical Formula 2 below.

[0020] [Chemical formula 2]

[0021] [A 1-ax (B1 1-m B2 m ) x ](M1 1-n M2 n ) 3

[0022] In the chemical formula 2, the A may include an alkali metal element, the B1 and the B2 may be different from each other and may each independently include at least one selected from magnesium (Mg), aluminum (Al), gallium (Ga), silicon (Si), germanium (Ge), tin (Sn), arsenic (As), antimony (Sb), and combinations thereof, the M1 and the M2 may be different from each other and may each independently include at least one selected from niobium (Nb), tantalum (Ta), boron (B), zirconium (Zr), phosphorus (P), and combinations thereof, the oxidation numbers of the B1 and the B2 may be the same, the a may be the oxidation number of the B1 or the B2, and may satisfy 0≤m≤1, 0≤n≤1, and 0.01≤x≤0.3.

[0023] The composite positive active material may include 98 wt % to 99.9 wt % of the core portion and 0.1 wt % to 2 wt % of the shell portion.

[0024] The alkali metal oxide may have a trigonal crystal structure, and may belong to an R3c space group.

[0025] The alkali metal element and the substituent element may occupy a Wyckoff position 6a (0, 0, 0.283).

[0026] The substituent element may not occupy the Wyckoff position 6a (0, 0, 0).

[0027] As the substituting element replaces a portion of the alkali metal element, the lattice volume of the alkali metal oxide may be reduced compared to when the substituting element is not present.

[0028] As the substituting element replaces a portion of the alkali metal element, the length of the a-axis of the alkali metal oxide obtained by Rietveld analysis of X-ray diffraction may be reduced compared to when the substituting element is not present.

[0029] As the substituent element replaces a portion of the alkali metal element, the length of the c-axis of the alkali metal oxide obtained by Rietveld analysis of X-ray diffraction may increase compared to when the substituent element is not present.

[0030] As the substitution element replaces a portion of the alkali metal element, the Bragg angle of at least one (hkl) diffraction peak of the alkali metal oxide among (012), (104), (110) and (113) obtained by Rietveld analysis of X-ray diffraction may shift to a higher angle compared to when the substitution element is not present.

[0031] The shell portion may be a conformal layer.

[0032] As the substituent element replaces a portion of the alkali metal element, the adsorption energy (E) of the alkali metal oxide to the core portion is increased compared to when the substituent element is not present. ads ) can be increased.

[0033] As the substituting element replaces a portion of the alkali metal element, the activation energy barrier of the alkali metal oxide may be lowered compared to when the substituting element is not present.

[0034] According to one embodiment of the present invention, a method for preparing a composite positive electrode active material for a lithium secondary battery may include the following steps: preparing a core portion capable of inserting and extracting lithium; preparing a raw material of an alkali metal oxide; adding the core portion and the raw material to a solvent and stirring to obtain an intermediate substance; drying the intermediate substance; and heat-treating the dried intermediate substance.

[0035] The raw material may include alkoxides of respective elements constituting the alkali metal oxide.

[0036] According to one embodiment of the present invention, a method for preparing a composite positive electrode active material for a lithium secondary battery may include the following steps: preparing a raw material of an alkali metal oxide; pulverizing the raw material with a ball mill to obtain a pulverized product; heat-treating the pulverized product to obtain an alkali metal oxide; and forming a shell portion containing the alkali metal oxide on the surface of a core portion capable of inserting and extracting lithium.

[0037] The raw material may include oxides of respective elements constituting the alkali metal oxide.

[0038] In the step of obtaining the pulverized product, the raw material may be pulverized by a high-energy ball milling method.

[0039] (III) Beneficial effects

[0040] According to the present invention, a composite positive electrode active material for a lithium secondary battery capable of reducing high interface resistance between a positive electrode active material and a solid electrolyte and a method for preparing the same can be obtained.

[0041] According to the present invention, a composite positive electrode active material for lithium secondary batteries having high chemical adsorption strength and chemical stability and a preparation method thereof can be obtained.

[0042] According to the present invention, a composite positive electrode active material for a lithium secondary battery having excellent lithium ion conductivity and a preparation method thereof can be obtained.

[0043] The effects of the present invention are not limited to the effects mentioned above. It should be understood that the effects of the present invention include all effects that can be inferred from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A lithium secondary battery according to the present invention is shown.

[0045] Figure 2 The composite positive electrode active material according to the present invention is shown.

[0046] Figure 3 These are the results of X-ray diffraction analysis of the alkali metal oxides according to Preparation Example 1 and Comparative Preparation Example 1.

[0047] Figure 4This is the result of Rietveld analysis of the alkali metal oxide according to Preparation Example 1.

[0048] Figure 5 This is the result of Rietveld analysis of the alkali metal oxide according to Comparative Preparation Example 1.

[0049] Figure 6 This is the result of X-ray photoelectron spectroscopy (XPS) of Nb 3d of the alkali metal oxide according to Preparation Example 1.

[0050] Figure 7 It is the result of X-ray photoelectron spectroscopy (XPS) of Nb 3d of the alkali metal oxide according to Comparative Preparation Example 1.

[0051] Figure 8 These are the results of X-ray photoelectron spectroscopy (XPS) analysis of the alkali metal oxide according to Preparation Example 1 in the binding energy range of 0-100 eV.

[0052] Fig. 9 These are the results of analyzing the alkali metal oxide according to Comparative Preparation Example 1 by X-ray photoelectron spectroscopy (XPS) in the binding energy range of 0-100 eV.

[0053] Fig.10 It is the calculation result of the stable potential window of the alkali metal oxide according to Preparation Example 1 and Comparative Preparation Example 1.

[0054] Fig.11 These are the results of X-ray diffraction analysis of the alkali metal oxides according to Preparation Example 2 and Comparative Preparation Example 2.

[0055] Fig.12a The results of analyzing the composite positive electrode active material according to Preparation Example 3 by high resolution transmission electron microscopy (HR-TEM) are shown in FIG.

[0056] Figure 12b is with Fig.12a Compare the results of changing the magnification.

[0057] Fig.13a The composite positive electrode active material according to Comparative Preparation Example 3 was analyzed by high-resolution transmission electron microscopy (HR-TEM).

[0058] Fig.13b is with Fig.13a Compare the results of changing the magnification.

[0059] Fig.14The results of analyzing the composite positive electrode active material according to Preparation Example 3 by high-resolution transmission electron microscopy-energy dispersive spectroscopy (HR-TEM-EDS) are shown in FIG.

[0060] Fig.15 It is the C-rate experimental result of the lithium ion battery according to Example 1.

[0061] Fig.16 This is the C rate test result of the lithium ion battery according to Comparative Example 1.

[0062] Fig.17 These are the measurement results of the lifespan and coulombic efficiency of the lithium ion battery according to Example 1.

[0063] Fig.18 These are the measurement results of the lifespan and coulombic efficiency of the lithium ion battery according to Comparative Example 1.

[0064] Fig.19 These are the evaluation results of the electrochemical characteristics of the all-solid-state battery according to Example 2.

[0065] Fig. 20 These are the evaluation results of the electrochemical characteristics of the all-solid-state battery according to Comparative Example 2.

[0066] Description of reference numerals:

[0067] 10: Positive electrode 20: Negative electrode 30: Solid electrolyte layer

[0068] 100: composite positive electrode active material 110: core 120: shell DETAILED DESCRIPTION

[0069] Through the accompanying drawings and the related preferred embodiments below, the above-mentioned purpose, other purposes, features and advantages of the present invention can be easily understood. However, the present invention is not limited to the embodiments described herein, and the present invention can also be implemented by other embodiments. In addition, the embodiments described herein are provided in order to make the disclosed content sufficient and complete and to fully convey the idea of ​​the present invention to those skilled in the art.

[0070] When describing the drawings, similar reference numerals are used for similar constituent elements. In the drawings, for the clarity of the present invention, the size of the structure is shown enlarged than the actual size. The terms first, second, etc. can be used to describe various constituent elements, but the above-mentioned constituent elements should not be limited to the terms. The terms are used only for the purpose of distinguishing one constituent element from another constituent element. For example, without departing from the scope of the present invention, the first constituent element can be named as the second constituent element, and similarly, the second constituent element can also be named as the first constituent element. Unless otherwise clearly stated in the text, the singular expression includes the plural expression.

[0071] It should be understood that, in this specification, the terms "comprise", "include" or "have" are used to specify the existence of features, numbers, steps, operations, constituent elements, parts or combinations thereof recorded in the specification, and do not preclude the existence or additional possibility of one or more other features, numbers, steps, operations, constituent elements, parts or combinations thereof. In addition, when describing a layer, film, region, plate or other part as being "on" another part, this includes not only the case where it is "directly" "above" another part, but also the case where other parts exist in the middle. On the other hand, when describing a layer, film, region, plate or other part as being "below" another part, this includes not only the case where it is "directly" "below" another part, but also the case where other parts exist in the middle.

[0072] With respect to all the numbers, values ​​and / or expressions used in this specification that represent the amount of ingredients, reaction conditions, polymer compositions and mixtures, unless otherwise stated, these numbers are approximate values ​​that reflect the various uncertainties of measurement that occur when obtaining these values ​​from essentially different matters, and therefore should be understood to be modified by the term "about" in all cases. In addition, when numerical ranges are disclosed in this specification, these ranges are continuous and, unless otherwise stated, include all values ​​from the minimum value to the maximum value of these ranges. Further, when these ranges refer to integers, unless otherwise stated, all integers from the minimum value to the maximum value are included.

[0073] Figure 1 A lithium secondary battery according to the present invention is shown. The lithium secondary battery may include an all-solid-state battery. The lithium secondary battery may include a positive electrode (cathode) 10, a negative electrode (anode) 20, and a solid electrolyte layer 30 located between the positive electrode 10 and the negative electrode 20.

[0074] The positive electrode 10 may include a composite positive electrode active material, a first solid electrolyte, a first conductive material, a first binder, and the like.

[0075] Figure 2Disclosed is a composite positive electrode active material 100 according to the present invention. The composite positive electrode active material 100 may include a core part 110 and a shell part 120 covering the surface of the core part 110.

[0076] The core part 110 may include a lithium transition metal oxide into which lithium is inserted and from which lithium is extracted.

[0077] As long as the lithium transition metal oxide is a conventional lithium transition metal oxide in the technical field to which the present invention pertains, any lithium transition metal oxide may be included. For example, the lithium transition metal oxide may include LiNi x1 Co X2 Mn X3 O 2 (0.65 ≤ x1 ≤ 0.85, 0.05 < x2 < 0.25, 0.03 < x3 < 0.2, and x1 + x2 + x3 = 1).

[0078] The core part 110 may be in the form of secondary particles aggregated from primary particles containing the lithium transition metal oxide. The primary particles may refer to the smallest particle units that are distinguishable as one lump when observing a cross-section of the core part 110 through equipment such as a Scanning Electron Microscope (SEM). The primary particles may be composed of one grain or multiple grains. The secondary particles may refer to a structure formed by aggregation of multiple primary particles. The shape of the secondary particles is not particularly limited and may be, for example, spherical or elliptical.

[0079] The average particle diameter (D50) of the core part 110 is not particularly limited and may be, for example, 1 μm to 20 μm. The average particle diameter (D50) of the core part 110 can be measured using a commercially available laser diffraction scattering type particle size distribution measuring instrument, for example, using a Microtrac particle size distribution measuring device. In addition, 200 particles can be arbitrarily extracted from an electron microscope photograph and the average particle diameter can be calculated.

[0080] The shell part 120 may include an alkali metal oxide.

[0081] The alkali metal oxide may include an alkali metal element, a transition metal element, and a substitution element. The substitution element may include an element that substitutes a part of the alkali metal element and has an oxidation number higher than that of the alkali metal element.

[0082] The alkali metal element may transfer lithium ions released from the core part 110 at the interface between the solid electrolyte and the shell part 120 in the positive electrode 10 and at the interface between the shell part 120 and the core part 110.

[0083] The alkali metal element may include at least one selected from lithium (Li), sodium (Na), potassium (K), and combinations thereof. Preferably, the alkali metal element may include lithium (Li).

[0084] In the present invention, the alkali metal element is substituted with a substituent element having a higher oxidation number than the alkali metal element, thereby forming vacancies for maintaining the electrical neutrality of the alkali metal oxide, thereby improving the lithium ion conductivity of the shell 120 .

[0085] The substituting element may include a non-transition metal with a fixed oxidation number. Wherein, a fixed oxidation number may refer to an oxidation number that does not change when forming a compound with a specific element. For example, the substituting element may refer to an element that reacts in a form with a fixed oxidation number when combined with a specific element such as lithium (Li), although multiple oxidation numbers may exist in theory. Since the substituting element has a fixed oxidation number, unlike a transition metal, the ionic radius will not change outside the fixed oxidation number range.

[0086] The substitution element may replace the position of the alkali metal element. In the past, many attempts have been made to substitute and / or dope the compound constituting the coating of the positive electrode active material with various elements, but the difference from the present invention is that the object of substitution and / or doping is a transition metal element rather than an alkali metal element.

[0087] The position where the substituent element is introduced can be adjusted by appropriately changing the type of the raw material of the alkali metal oxide and the composition of the raw material.

[0088] The substitution element replaces the position of the alkali metal element, does not react with surrounding elements during the operation of the lithium secondary battery, and is firmly combined with other elements in the crystal structure, so that the physicochemical stability of the shell 120 can be improved. Therefore, the stability of the interface between the solid electrolyte and the shell 120 and the interface between the shell 120 and the core 110 can be improved. In addition, since the side reaction caused by the shell 120 does not occur, the electrochemical characteristics of the lithium secondary battery can be improved.

[0089] The substituent element can stabilize the oxygen of the alkali metal oxide during the charge and discharge process of the lithium secondary battery. 1- Thermodynamically, it has a tendency to become stable by reducing the coordination with the surrounding cations. The substituent element can effectively stabilize the oxygen without changing the binding structure of the alkali metal element and the oxygen element. The substituent element can prevent the oxygen element from leaking or losing from the alkali metal oxide, thereby greatly improving the stability of the shell 120.

[0090] The substituent element is a non-transition metal with a fixed oxidation number, and may include any element as long as it is an element with an oxidation number higher than that of the alkali metal element, and may preferably include at least one selected from magnesium (Mg), aluminum (Al), gallium (Ga), silicon (Si), germanium (Ge), tin (Sn), antimony (Sb), arsenic (As) and combinations thereof. More preferably, the substituent element may include magnesium (Mg).

[0091] The transition metal element may include any transition metal element as long as it is a transition metal element included in the alkali metal oxide commonly used in the technical field to which the present invention belongs. For example, the transition metal element may include at least one selected from niobium (Nb), tantalum (Ta), zirconium (Zr) and a combination thereof.

[0092] However, the alkali metal oxide may contain a non-metallic element instead of the transition metal element or together with the transition metal element. The non-metallic element is not particularly limited, but, for example, may contain at least one selected from boron (B), phosphorus (P) and a combination thereof.

[0093] The alkali metal oxide may include a compound represented by Chemical Formula 1 below.

[0094] [Chemical formula 1]

[0095] (A 1-ax B x )MO 3

[0096] In the Chemical Formula 1, the A may include an alkali metal element.

[0097] The B may include at least one selected from magnesium (Mg), aluminum (Al), gallium (Ga), silicon (Si), germanium (Ge), tin (Sn), antimony (Sb), arsenic (As), and combinations thereof.

[0098] The M may include at least one selected from niobium (Nb), tantalum (Ta), boron (B), zirconium (Zr), phosphorus (P), and combinations thereof.

[0099] The a may be the oxidation number of B.

[0100] The x may satisfy 0.01≤x≤0.3.

[0101] When x is less than 0.01, the effect of improving the physicochemical stability of the alkali metal oxide cannot be obtained. When x exceeds 0.3, the molar number of the alkali metal element is lower than the required molar number, so the transfer of lithium ions in the shell 120 may not be smooth.

[0102] The alkali metal oxide may include a compound represented by Chemical Formula 2 below.

[0103] [Chemical formula 2]

[0104] [A 1-ax (B1 1-m B2 m ) x ](M1 1-n M2 n ) 3

[0105] In the Chemical Formula 2, the A may include an alkali metal element.

[0106] The B1 and the B2 may be different from each other and may each independently include at least one selected from magnesium (Mg), aluminum (Al), gallium (Ga), silicon (Si), germanium (Ge), tin (Sn), antimony (Sb), arsenic (As), and combinations thereof.

[0107] The M1 and the M2 may be different from each other, and may each independently include at least one selected from niobium (Nb), tantalum (Ta), boron (B), zirconium (Zr), phosphorus (P), and combinations thereof.

[0108] The oxidation numbers of the B1 and the B2 may be the same.

[0109] The a may be the oxidation number of the B1 or the B2.

[0110] The m, n and x may satisfy 0≤m≤1, 0≤n≤1 and 0.01≤x≤0.3, respectively.

[0111] The composite positive electrode active material 100 may include 98 wt % to 99.9 wt % of the core 110 and 0.1 wt % to 2 wt % of the shell 120. When the content of the shell 120 is less than 0.1 wt %, the effect of introducing the shell 120 cannot be obtained, and when the content of the shell 120 exceeds 2 wt %, the shell 120 becomes thicker, thereby possibly hindering the conduction of lithium ions. In addition, as in the present invention, when the shell 120 is formed with an alkali metal oxide according to the chemical formula 1 and / or the chemical formula 2, the shell 120 can be formed into a conformal layer, so that a uniform and high coverage shell 120 can be obtained even at a content of less than 2 wt %. This is described below.

[0112] The preparation method of the composite positive electrode active material 100 is not particularly limited, and the composite positive electrode active material 100 may be prepared by various methods such as a liquid phase method and a solid phase method.

[0113] The liquid phase method may include the steps of: preparing the core; preparing a raw material of an alkali metal oxide; adding the core and the raw material into a solvent and stirring to obtain an intermediate substance; drying the intermediate substance; and heat-treating the dried intermediate substance.

[0114] The raw material may include the alkali metal element, the transition metal element (and / or non-metal element) and the alkoxide of the substituent element. For example, the raw material may include lithium ethoxide, niobium ethoxide, magnesium ethoxide, etc.

[0115] By adjusting the type, content, ratio, etc. of the components of the raw materials, the substitution element can replace the alkali metal element and occupy the position of the alkali metal element instead of replacing the transition metal element.

[0116] The type of the solvent is not particularly limited, and may include organic solvents such as alcohol, water-based solvents, and the like.

[0117] The solid phase method may include the following steps: preparing a raw material of an alkali metal oxide; pulverizing the raw material using a ball mill to obtain a pulverized product; heat-treating the pulverized product to obtain an alkali metal oxide; and forming a shell portion including the alkali metal oxide on the surface of the core portion.

[0118] The raw material may include the alkali metal element, the transition metal element (and / or non-metal element) and the oxide of the substituent element. For example, the raw material may include lithium carbonate, niobium oxide, magnesium oxide, etc.

[0119] In the step of obtaining the pulverized product, the raw material can be pulverized by high-energy grinding. The method, device, conditions, etc. of the high-energy grinding method are not particularly limited, and a high-energy planetary ball mill capable of high-speed revolution and rotation can be used.

[0120] The first solid electrolyte may be responsible for movement of lithium ions in the positive electrode 10 .

[0121] The first solid electrolyte may include at least one selected from an oxide-based solid electrolyte, a sulfide-based solid electrolyte, and a combination thereof. In addition, the solid electrolyte may be crystalline, amorphous, or a mixture thereof.

[0122] The oxide-based solid electrolyte may include a LLTO (Li-La-Ti-oxide)-based solid electrolyte having a perovskite structure, a LATP (Li-Al-Ti-P)-based solid electrolyte having a sodium super ion conductor (NASICON) structure, or the like.

[0123] The sulfide-based solid electrolyte may include Li 2 SP 2 S 5 , Li 2 SP 2 S 5 -LiI, Li 2 SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 -Li 2 O. Li 2 SP 2 S 5 -Li 2 O-LiI、Li 2 S-SiS 2 , Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 SB 2 S 3 , Li 2 SP 2 S 5 -Z m S n (where m and n are positive numbers, and Z is one of Ge, Zn, and Ga), Li 2 S-GeS 2 , Li 2 S-SiS 2 -Li 3 PO4 , Li 2 S - SiS 2 -Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, In), Li 10 GeP 2 S 12 etc.

[0124] Preferably, the first solid electrolyte may include a sulfide - based solid electrolyte having a thiogermanate crystal structure. The sulfide - based solid electrolyte having a thiogermanate crystal structure may include at least one selected from Li 7-y PS 6-y Ha y (Ha includes Cl, Br or I, and satisfies 0 < y ≤ 2), Li 7-z PS 6-z (Ha1 1-b Ha2 b ) z (Ha1 and Ha2 are different from each other and each independently includes Cl, Br or I, and satisfies 0 < b < 1 and 0 < z ≤ 2) and combinations thereof.

[0125] The first conductive material may include carbon black, conductive graphite, acetylene black, graphene, carbon nanotube, carbon nanofiber, vapor grown carbon fiber, etc.

[0126] The first binder may include butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. The first binder may exist in the form of particles, wires, etc. in the positive electrode 10.

[0127] The positive electrode 10 may include 70 wt % to 90 wt % of the composite positive electrode active material, 10 wt % to 15 wt % of the first solid electrolyte, 1 wt % to 5 wt % of the first conductive material, and 1 wt % to 5 wt % of the first binder. However, the content of each component may be appropriately adjusted in consideration of the desired capacity, efficiency, etc. of the all-solid-state battery.

[0128] The thickness of the positive electrode 10 is not particularly limited, but may be 1 μm to 100 μm. The thickness of the positive electrode 10 may refer to an average value when measuring 5 points of a measurement object. In addition, the thickness of the positive electrode 10 may refer to the thickness of the lithium secondary battery when it is discharged.

[0129] According to the first embodiment of the present invention, the negative electrode 20 may be a composite negative electrode including a negative electrode active material, a second solid electrolyte, a second conductive material, a second binder, and the like.

[0130] The negative electrode active material is not particularly limited, and may be, for example, a carbon active material or a metal active material.

[0131] The carbon active material may be graphite such as mesocarbon microbeads (MCMB), highly oriented graphite (highly oriented pyrolytic graphite (HOPG)), or amorphous carbon such as hard carbon and soft carbon.

[0132] The metal active material may be indium (In), aluminum (Al), silicon (Si), tin (Sn), an alloy containing at least one of these elements, or the like.

[0133] The negative electrode active material may be a composite of the carbon active material and the metal active material. For example, the surface of the carbon active material may be coated with the metal active material or the surface of the metal active material may be coated with the carbon active material.

[0134] The second solid electrolyte may be responsible for movement of lithium ions in the negative electrode 20 .

[0135] The second solid electrolyte may include at least one selected from an oxide-based solid electrolyte, a sulfide-based solid electrolyte, and a combination thereof. In addition, the solid electrolyte may be crystalline, amorphous, or a mixture thereof.

[0136] The oxide-based solid electrolyte may include an LLTO (Li-La-Ti-oxide)-based solid electrolyte having a perovskite structure, an LATP (Li-Al-Ti-P)-based solid electrolyte having a sodium superion conductor structure, and the like.

[0137] The sulfide-based solid electrolyte may include Li2 SP 2 S 5 , Li 2 SP 2 S 5 -LiI, Li 2 SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 -Li 2 O. Li 2 SP 2 S 5 -Li 2 O-LiI、Li 2 S-SiS 2 , Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 SB 2 S 3 , Li 2 SP 2 S 5 -Z m S n (where m and n are positive numbers, and Z is one of Ge, Zn, and Ga), Li 2 S-GeS 2 , Li 2 S-SiS 2 -Li 3 PO 4 , Li 2 S-SiS 2 -Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In), Li 10 G 2 S 12etc.

[0138] Preferably, the second solid electrolyte may include a sulfide-based solid electrolyte having a thiogermanate crystal structure. The sulfide-based solid electrolyte having a thiogermanate crystal structure may include a selection from Li 7-y PS 6-y Ha y (where Ha includes Cl, Br, or I and satisfies 0 < y ≤ 2), Li 7-z PS 6-z (Ha1 1-b Ha2 b ) z (where Ha1 and Ha2 are different from each other and each independently includes Cl, Br, or I, and satisfy 0 < b < 1 and 0 < z ≤ 2) and at least one of their combinations.

[0139] The second solid electrolyte may be the same as or different from the first solid electrolyte.

[0140] The second conductive material may include carbon black, conductive graphite, ethylene black, graphene, carbon nanotubes, carbon nanofibers, vapor-grown carbon fibers, etc.

[0141] The second conductive material may be the same as or different from the first conductive material.

[0142] The second binder may include butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. The second binder may be present in the negative electrode 20 in the form of granules, wires, etc.

[0143] The second binder may be the same as or different from the first binder.

[0144] The negative electrode 20 may include 80 wt% to 85 wt% of the negative electrode active material, 10 wt% to 15 wt% of the second solid electrolyte, and 1 wt% to 5 wt% of the second binder. However, the content of each component may be appropriately adjusted in consideration of the desired capacity, efficiency, etc. of the all-solid-state battery.

[0145] The thickness of the negative electrode 20 is not particularly limited, but may be 1 μm to 100 μm. The thickness of the negative electrode 20 may refer to the average value when measuring 5 points of the measurement object. In addition, the thickness of the negative electrode 20 may refer to the thickness during discharge of the lithium secondary battery.

[0146] According to the second embodiment of the present invention, the negative electrode 20 may include lithium metal or a lithium metal alloy.

[0147] The lithium metal alloy may include an alloy of lithium and a metal or metalloid that can be alloyed with lithium. The metal or metalloid that can be alloyed with lithium may include silicon (Si), tin (Sn), aluminum (Al), germanium (Ge), lead (Pb), bismuth (Bi), antimony (Sb), etc.

[0148] According to the third embodiment of the present invention, the negative electrode 20 may not include a negative electrode active material and a structure that substantially plays the same role as the negative electrode active material. When the all-solid-state battery is charged, lithium ions moving from the positive electrode 10 are precipitated and stored in the form of lithium metal between the negative electrode 20 and the negative electrode current collector (not shown).

[0149] The negative electrode 20 may include amorphous carbon and a metal that can form an alloy with lithium.

[0150] The amorphous carbon may include at least any one selected from furnace black, acetylene black, ketjen black, graphene, and a combination thereof.

[0151] The metal may include at least any one selected from gold (Au), platinum (Pt), palladium (Pd), silicon (Si), silver (Ag), aluminum (Al), bismuth (Bi), tin (Sn), zinc (Zn), and combinations thereof.

[0152] The negative electrode 20 may include 90 to 99 wt % of the amorphous carbon and 1 to 10 wt % of the metal. However, the content of each component may be appropriately adjusted in consideration of the desired capacity, efficiency, etc. of the all-solid-state battery.

[0153] The solid electrolyte layer 30 may be in the form of a sheet having at least two opposing main surfaces. The two main surfaces may each include not only a mathematical plane but also a specified curved surface in part, and may also have concavities and convexities generated when the solid electrolyte layer 30 is prepared. In this sense, the sheet is not limited to a relatively thin rectangular parallelepiped.

[0154] In the sheet-like solid electrolyte layer 30, the interval between the two opposing main surfaces may be the thickness of the solid electrolyte layer 30. The length of the first direction (e.g., width direction) perpendicular to the thickness direction of the solid electrolyte layer 30 is greater than the thickness. In addition, the length of the second direction (e.g., length direction) perpendicular to the thickness direction and the first direction of the solid electrolyte layer 30 is greater than the thickness.

[0155] The thickness of the solid electrolyte layer 30 is not particularly limited, but may be 1 μm to 100 μm. The thickness of the solid electrolyte layer 30 may refer to an average value when measuring 5 points of a measurement object.

[0156] The solid electrolyte layer 30 may include a third solid electrolyte having lithium ion conductivity, a third binder, and the like.

[0157] The third solid electrolyte may include at least one selected from an oxide-based solid electrolyte, a sulfide-based solid electrolyte, and a combination thereof. In addition, the solid electrolyte may be crystalline, amorphous, or a mixed state thereof.

[0158] The oxide-based solid electrolyte may include an LLTO (Li-La-Ti-oxide)-based solid electrolyte having a perovskite structure, an LATP (Li-Al-Ti-P)-based solid electrolyte having a sodium superion conductor structure, and the like.

[0159] The sulfide-based solid electrolyte may include Li 2 SP 2 S 5 , Li 2 SP 2 S 5 -LiI, Li 2 SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 -Li 2 O. Li 2 SP 2 S 5 -Li 2 O-LiI、Li 2 S-SiS 2 , Li 2 S-SiS 2 -LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 -LiI, Li 2 S-SiS 2 -P 2 S 5 -LiI, Li 2 SB 2 S 3 , Li 2 SP 2S 5 -Z m S n (wherein, m and n are positive numbers, and Z is one of Ge, Zn, and Ga), Li 2 S - GeS 2 、Li 2 S - SiS 2 -Li 3 PO 4 、Li 2 S - SiS 2 -Li x MO y (wherein, x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, and In), Li 10 GeP 2 S 12 etc.

[0160] Preferably, the third solid electrolyte may include a sulfide - based solid electrolyte having a thiogalena crystal structure. The sulfide - based solid electrolyte having a thiogalena crystal structure may include at least one selected from Li 7-y PS 6-y Ha y (Ha includes Cl, Br, or I, and satisfies 0 < y ≤ 2), Li 7-z PS 6-z (Ha1 1-b Ha2 b ) z (Ha1 and Ha2 are different from each other and each independently includes Cl, Br, or I, and satisfies 0 < b < 1 and 0 < z ≤ 2) and combinations thereof.

[0161] The third solid electrolyte may be the same as or different from the first and second solid electrolytes.

[0162] The third binder may include butadiene rubber, nitrile rubber, hydrogenated nitrile rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), etc. The third binder may be present in the solid electrolyte layer 30 in the form of particles, wires, etc.

[0163] The third binder may be the same as or different from the first and second binders.

[0164] Hereinafter, other embodiments of the present invention will be described more specifically by way of examples. The following examples are merely examples to facilitate the understanding of the present invention, and the scope of the present invention is not limited thereto.

[0165] Preparation Example 1

[0166] Prepared as follows from Li 0.9 Mg 0.05 NbO 3 Represents an alkali metal oxide.

[0167] As raw materials, lithium ethoxide, niobium ethoxide, and magnesium ethoxide are weighed and prepared according to the composition of the alkali metal oxide.

[0168] The raw materials are added to anhydrous ethyl alcohol as a solvent, and stirred at about 70° C. at a speed of about 300 rpm to obtain an intermediate material.

[0169] The intermediate material was dried using a vacuum oven at about 80° C. for about 12 hours.

[0170] The dried intermediate material is added into a box furnace, oxygen is injected into the box furnace at a flow rate of about 0.5 L / min, and the temperature of the box furnace is increased to about 300° C. at a rate of about 2° C. / min, and then the dried intermediate material is heat-treated for about 5 hours to obtain the alkali metal oxide.

[0171] Comparative Preparation Example 1

[0172] The alkali metal oxide was prepared by the same method as in Preparation Example 1, except that the raw material was changed so that the composition of the alkali metal oxide was LiNbO 3 Specifically, as the raw material, according to LiNbO 3 Lithium ethoxide and niobium ethoxide were weighed to prepare a composition of the present invention, and then the same stirring, drying and heat treatment as in Preparation Example 1 were performed.

[0173] Figure 3 These are the results of X-ray diffraction analysis of the alkali metal oxides of Preparation Example 1 and Comparative Preparation Example 1. Figure 3 It can be seen that even if the magnesium element as a substituting element in the alkali metal oxide according to Preparation Example 1 replaces the lithium element as an alkali metal element, the same crystal structure as that of Comparative Preparation Example 1 is well maintained. In addition, it can be seen that the alkali metal oxide according to the Preparation Example 1 has a trigonal crystal structure and belongs to the R3c space group.

[0174] Based on the results of the X-ray diffraction analysis of the alkali metal oxides according to Preparation Example 1 and Comparative Preparation Example 1, Rietveld analysis was performed to confirm the crystal structure of each compound in more detail.

[0175] Figure 4 This is the result of Rietveld analysis of the alkali metal oxide according to Preparation Example 1. Figure 5 This is the result of Rietveld analysis of the alkali metal oxide according to Comparative Preparation Example 1. Figure 4 and Figure 5 Shows Figure 3 The X-ray diffraction analysis results are consistent with the trend.

[0176] Will Figure 4 The results are detailed in Table 1 below. Figure 5 The results are detailed in Table 2 below.

[0177] [Table 1]

[0178]

[0179] [Table 2]

[0180]

[0181] In Tables 1 and 2, the parentheses on the right side of each numerical value may refer to a standard deviation.

[0182] Referring to Table 1, in the alkali metal oxide according to Preparation Example 1, Li as an alkali metal element and Mg as a substitution element occupy Wyckoff position 6a (0, 0, 0.283) together. The occupancy of the alkali metal element is about 90%, and the occupancy of the substitution element is about 5.5%.

[0183] In addition, in the alkali metal oxide according to Preparation Example 1, Mg as a substituent element does not occupy the Wyckoff position 6a (0, 0, 0). This can be seen from the fact that the occupancy rate of Mg2 in 6a (0, 0, 0) in Table 1 is 0%.

[0184] From the above results, it was confirmed that magnesium (Mg) as the substituting element substituted lithium (Li) as the alkali metal element instead of niobium (Nb) as the transition metal element.

[0185] The lattice volumes and the like of the alkali metal oxides according to Preparation Example 1 and Comparative Preparation Example 1 can be confirmed by Rietveld analysis and are shown in Table 3 below.

[0186] [Table 3]

[0187]

[0188] Compared with the alkali metal oxide without the substitution element in Comparative Preparation Example 1, the unit lattice volume, LiO 6 The volume of the octahedron decreases. This is because the magnesium ion (Mg 2+ ) has a smaller ionic radius than lithium ions (Li +) ion radius. In addition, it can be seen that due to the difference in ionic radius between the alkali metal element and the substituent element, the length of the a-axis of the unit lattice of Preparation Example 1 is reduced and the length of the c-axis is increased compared with Comparative Preparation Example 1. In addition, based on the same reason, it can be confirmed that the O-Li-O angle along the a-axis of Preparation Example 1 is smaller than the O-Li-O angle along the a-axis of Comparative Preparation Example 1, and the O-Li-O angle along the c-axis of Preparation Example 1 is greater than the O-Li-O angle along the c-axis of Comparative Preparation Example 1.

[0189] In addition, as the a-axis length of the unit cell of the alkali metal element of Preparation Example 1 decreases and the c-axis length increases, the peak shift phenomenon occurs in the Rietveld analysis results. Specifically, compared with Comparative Preparation Example 1, it can be observed that the Bragg angle of at least one (hkl) diffraction peak among (012), (104), (110) and (113) obtained by Rietveld analysis of Preparation Example 1 shifts to a high angle. The Bragg angles of each diffraction peak are recorded in Table 4 below.

[0190] [Table 4]

[0191] HkD Bragg angle [2θ] of Preparation Example 1 Bragg angle [2θ] of comparative preparation example 1 (012) 23.7344 23.7123 (104) 32.7075 32.6966 (110) 34.8906 34.8388 (006) 38.9172 38.9313 (113) 40.1144 40.0718

[0192] Since the rate of change of the c-axis length change (+0.03%) relative to the a-axis length change (-0.14%) between Preparation Example 1 and Comparative Preparation Example 1 is very small, as shown in Table 4, it can be seen that all peaks except the hkl (006) peak which is only affected by the change in the c-axis length are shifted to high angles.

[0193] Figure 6 It is the result of X-ray photoelectron spectroscopy (XPS) of Nb 3d of the alkali metal oxide according to Preparation Example 1. Figure 7 is the result of X-ray photoelectron spectroscopy (XPS) of Nb 3d of the alkali metal oxide according to Comparative Preparation Example 1. Figure 6 and Figure 7 The peak of does not change, and it can be seen that magnesium (Mg) as a substituent element has no effect on niobium (Nb) as a transition metal element.

[0194] Figure 8 These are the results of X-ray photoelectron spectroscopy (XPS) analysis of the alkali metal oxide according to Preparation Example 1 in the binding energy range of 0-100 eV. Fig. 9 is the result of X-ray photoelectron spectroscopy (XPS) analysis of the alkali metal oxide according to Comparative Preparation Example 1 in the binding energy range of 0-100 eV. Figure 8 Peaks due to Mg 2s and Mg 2p were found in the MgO2O3 matrix, indicating that the substituent element was well introduced into the alkali metal oxide according to Preparation Example 1.

[0195] Ab initio calculation was used to calculate the adsorption energy (E) at the interface when magnesium replaces the alkali metal element of the alkali metal oxide. ads ). The calculations were performed using the Vienna Ab initioSimulation Package (VASP) program.

[0196] The adsorption energy between the interfaces in this calculation (E abs ) is obtained as follows.

[0197] E ads =E 基材上的LMNO -[E 基材 +E LMNO ]

[0198] Here, the substrate refers to the adsorbed material, and in the present invention, it may refer to the core part or the solid electrolyte. LMNO may refer to the alkali metal oxide according to the present invention. 基材上的LMNO It can refer to the energy of the structure of alkali metal oxide adsorbed on the adsorbed material, E 基材 It can refer to the surface structure energy of the adsorbed material itself, E LMNO It may refer to the surface structure energy of the alkali metal oxide itself.

[0199] The adsorption energy to the core was calculated by increasing the proportion of magnesium (Mg) as a substituent element in the alkali metal oxide. A nickel-manganese-cobalt-based lithium oxide was used as the core. In addition, the adsorption energy to the solid electrolyte was calculated by increasing the proportion of magnesium (Mg) as a substituent element in the alkali metal oxide. Li 6 PS 5 Cl 0.5 Br 0.5 The results are shown in Table 5 below.

[0200] [Table 5]

[0201]

[0202] Referring to Table 5, in view of the fact that the adsorption energy of the alkali metal oxide according to the present invention in the presence of the substitution element to the core portion and the adsorption energy to the solid electrolyte are negative values, it can be predicted that the interface structure can be stably maintained. In addition, in view of the fact that the absolute value of the adsorption energy to the core portion increases with the increase in the proportion of the substitution element, it can be confirmed that the introduction of the substitution element is of great help to the interface stability. In addition, when the molar number of the substitution element exceeds 0.3, the adsorption energy to the solid electrolyte is reduced, from which it can be seen that an appropriate amount of substitution element needs to be introduced.

[0203] The factors affecting lithium ion conduction in alkali metal oxides, namely the activation barrier energy, were calculated by first-principles calculations. In this calculation, the activation barrier of the structure was obtained using the Nudged elastic band (NEB) method, and the calculation was performed after five intermediate phases were formed between each site. The results are shown in Table 6 below.

[0204] [Table 6]

[0205] category Activation energy barrier [meV] <![CDATA[LiNbO 3 ]]> 1091.30 <![CDATA[Li 0.666 Mg 0.167 No. 3 ]]> 1038.78 <![CDATA[Li 0.5 Mg 0.25 No. 3 ]]> 1038.79 <![CDATA[Li 0.34 Mg 0.33 No. 3 ]]> 1038.38

[0206] Referring to Table 6, as the substitution element is introduced, the activation energy barrier tends to decrease. Therefore, the alkali metal oxide according to the present invention can have higher lithium ion conductivity than the alkali metal oxide without the substitution element.

[0207] Fig.10 It is the calculation result of the stable potential window of the alkali metal oxide according to Preparation Example 1 and Comparative Preparation Example 1.

[0208] Each alkali metal oxide decomposes into lithium niobium oxide and oxygen in the high voltage region. However, in the low voltage region, it can be decomposed into lithium niobium oxides of different compositions. Further, it is predicted that magnesium oxide is formed in Preparation Example 1 according to the presence of the substitution element. Based on this prediction, the energy of each decomposition product is calculated and summarized, and is shown in Fig.10 middle.

[0209] As a result, Preparation Example 1 exhibits a wider potential window, and in particular, the stability at low voltage is greatly increased compared to Comparative Preparation Example 1. Through this potential window characteristic, it can be predicted that the alkali metal oxide according to the present invention exhibits improved interface stability in the low voltage region, that is, in a state where the concentration of lithium in the positive electrode is low.

[0210] Preparation Example 2

[0211] The solid phase method was used to prepare Li 0.9 Mg 0.05 NbO 3 Represents an alkali metal oxide.

[0212] As a raw material, lithium carbonate (LiCO) is weighed according to the composition of the alkali metal oxide. 2 CO 3 ), niobium oxide (Nb 2 O 5 ) and magnesium oxide (MgO) to prepare.

[0213] The raw material was charged into a high energy grinding device in an argon atmosphere and pulverized at about 400 rpm for about 12 hours to obtain a pulverized product.

[0214] The pulverized material is added to a box furnace, oxygen is injected into the box furnace at a flow rate of about 0.3 L / min, and the temperature of the box furnace is increased to about 850° C. at a rate of about 2° C. / min, and then the pulverized material is heat-treated for about 5 hours to obtain the alkali metal oxide.

[0215] Comparative Preparation Example 2

[0216] The alkali metal oxide was prepared by the same method as in Preparation Example 2, except that the raw materials were changed so that the composition of the alkali metal oxide was LiNbO 3 Specifically, as the raw material, according to LiNbO 3 Weigh the composition of lithium carbonate (Li 2 CO 3 ) and niobium oxide (Nb 2 O 5 ) is prepared, and then the same pulverization and heat treatment as Preparation Example 2 are carried out.

[0217] Fig.11 These are the results of X-ray diffraction analysis of the alkali metal oxides of Preparation Example 2 and Comparative Preparation Example 2. Fig.11 It can be seen that even if the magnesium element as a substituting element in the alkali metal oxide of Preparation Example 2 replaces the lithium element as an alkali metal element, the same crystal structure as that of Comparative Preparation Example 2 is well maintained. In addition, it can be confirmed that the substituting element can also be well introduced by a solid phase method (rather than a liquid phase method).

[0218] Preparation Example 3

[0219] The composite positive electrode active material comprising a core part and a shell part according to the present invention is prepared as follows. The composition of the alkali metal oxide constituting the shell part is Li 0.9 Mg 0.05 NbO 3 .

[0220] As raw materials, lithium ethoxide, niobium ethoxide, and magnesium ethoxide are weighed and prepared according to the composition of the alkali metal oxide.

[0221] The raw material and the core part are added to anhydrous ethanol as a solvent, and stirred at about 70° C. at a speed of about 300 rpm to obtain an intermediate substance. As the core part, a nickel-manganese-cobalt-based lithium oxide is used. In addition, the content of the raw material and the core part is adjusted so that the core part is 99% by weight and the shell part is 1% by weight based on the composite positive electrode active material as the final substance.

[0222] The intermediate material was dried using a vacuum oven at about 80° C. for about 12 hours.

[0223] The dried intermediate material is added to a box furnace, oxygen is injected into the box furnace at a flow rate of about 0.5 L / min, and the temperature of the box furnace is increased to about 300° C. at a rate of about 2° C. / min, and then the dried intermediate material is heat-treated for about 5 hours to obtain a composite positive active material.

[0224] Comparative Preparation Example 3

[0225] The composite positive electrode active material was prepared by the same method as in Preparation Example 3, except that the raw materials were changed so that the composition of the alkali metal oxide constituting the shell portion was LiNbO 3 Specifically, as the raw material, according to LiNbO 3 Lithium ethoxide and niobium ethoxide were weighed to prepare a composition of the present invention, and then stirring, drying and heat treatment were performed in the same manner as in Preparation Example 3 to obtain a composite positive electrode active material.

[0226] Fig.12a The results of analyzing the composite positive electrode active material according to Preparation Example 3 by high-resolution transmission electron microscopy (HR-TEM) are shown in FIG. Figure 12b is with Fig.12a Compare the results of changing the magnification.

[0227] Fig.13a The composite positive electrode active material according to Comparative Preparation Example 3 was analyzed by high-resolution transmission electron microscopy (HR-TEM). Fig.13b is with Fig.13a Compare the results of changing the magnification.

[0228] Reference Fig.13a , the shell of the composite positive electrode active material according to Comparative Preparation Example 3 is loosely formed and uneven. Fig.12a According to the composite positive electrode active material of Preparation Example 3, the shell portion is formed very uniformly and densely along the contour of the core portion. Figure 12b and Fig.13b This can be seen more clearly by comparing Figure 12b According to the shell of Preparation Example 3, the shell is very uniform and smooth without bumps or pinholes, etc. On the other hand, Fig.13b , it can be seen that for the shell of comparative preparation example 3, the shell surface itself has a curvature regardless of the contour of the core, and its thickness is uneven. It can be seen that by using the alkali metal oxide according to the present invention, the shell can be formed into a conformal layer. Among them, the conformal layer can refer to a series of layers whose surface is consistent with the contour of the coated material. In addition, the conformal layer can refer to a layered structure with excellent conformality, uniform thickness and high coverage of the coated material.

[0229] Fig.14 This is the result of analyzing the composite positive active material according to Preparation Example 3 by high-resolution transmission electron microscopy-energy dispersive spectroscopy (HR-TEM-EDS). When comparing the ratios of the elements in the composite positive active material, it can be seen that the substitution of the magnesium element in the shell is well achieved, and the magnesium is evenly distributed on the surface.

[0230] Example 1

[0231] A lithium ion battery was manufactured using the composite positive electrode active material according to Preparation Example 3 as follows.

[0232] The composite positive electrode active material, conductive material and binder were prepared in a mass ratio of 80:5:15 and added to N-methyl-2-pyrrolidone as a solvent to prepare a slurry. The slurry was coated on a substrate and dried to manufacture a positive electrode. Super-P was used as the conductive material, and polyvinylidene fluoride was used as the binder.

[0233] The positive electrode is laminated on one side of a separator containing glass fiber, and lithium foil is adhered on the other side to produce a structure. A liquid electrolyte is injected into the structure to complete a lithium ion battery. As the liquid electrolyte, LiPF 6 A liquid electrolyte dissolved at a concentration of about 1.15 M in an electrolyte solution comprising diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 2:4:4.

[0234] Comparative Example 1

[0235] A lithium ion battery was manufactured by the same method as in Example 1, except that the composite positive electrode active material according to Comparative Preparation Example 3 was used.

[0236] Fig.15 It is the C rate test result of the lithium ion battery according to Example 1. Fig.16 It is the C rate test result of the lithium ion battery according to Comparative Example 1. At a current density of 10mA / g, Example 1 exhibits a capacity of 217.4mAh / g, and Comparative Example 1 exhibits a capacity of 208.9mAh / g. This means that by introducing the substitution element, the interface resistance between the core and the shell is reduced. In addition, at a current density of 320mA / g, Example 1 and Comparative Example 1 exhibit capacities of 176.5mAh / g and 160.8mAh / g, respectively, so it can be seen that Example 1 also exhibits an effect of reducing interface resistance under high current density conditions.

[0237] Fig.17 These are the measurement results of the lifespan and coulombic efficiency of the lithium ion battery according to Example 1. Fig.18The results are based on the life and coulombic efficiency of the lithium-ion battery of Comparative Example 1. As a result of 100 cycles of charge and discharge at a current density of 200 mA / g, Example 1 and Comparative Example 1 showed a capacity retention rate of 92.6% and 79.4%, respectively. It can be seen that the long-term stability of the composite positive electrode active material can be improved by introducing an appropriate amount of substitution elements.

[0238] Example 2

[0239] An all-solid-state battery was manufactured using the composite positive electrode active material according to Preparation Example 3 as follows.

[0240] The composite positive electrode active material and the first solid electrolyte are prepared at a mass ratio of 70:30, and 1 part by weight of the first binder is prepared based on 100 parts by weight of the composite positive electrode active material and the first solid electrolyte. The first solid electrolyte is Li 6 PS 5 The sulfide-based solid electrolyte is represented by Cl. The binder is nitrile rubber.

[0241] The composite positive electrode active material and the first solid electrolyte are mixed with a mixing ball, and then mixed at about 1500 rpm for about 5 minutes. The binder is added to the product, and then mixed at about 1500 rpm for about 2 minutes. The mixing ball is removed and mixed at about 1500 rpm for about 1 minute. The product is added to a vacuum oven and dried at about 60° C. for about 24 hours to obtain a positive electrode material powder.

[0242] The positive electrode material powder is added into the mold so that the loading amount of the composite positive electrode active material is about 10.5 mg / cm 2 On top of it, about 120 mg of granulated Li as the third solid electrolyte was added. 6 PS 5 Cl was then subjected to a pressure of about 54 MPa to obtain a laminate of a positive electrode and a solid electrolyte layer. A lithium-indium alloy was adhered to the solid electrolyte layer to complete an all-solid-state battery.

[0243] Comparative Example 2

[0244] An all-solid-state battery was manufactured by the same method as in Example 2, except that the composite positive electrode active material according to Comparative Preparation Example 3 was used.

[0245] Fig.19 These are the evaluation results of the electrochemical characteristics of the all-solid-state battery according to Example 2. Fig. 20 These are the evaluation results of the electrochemical characteristics of the all-solid-state battery according to Comparative Example 2.

[0246] The measurement conditions are as follows.

[0247] - Confining pressure during charging and discharging: 10N / m 2

[0248] -Activation time: 3 hours

[0249] -Charging conditions: CC (~3.7V) - C / 20 and CV (3.7V) - limiting current is C / 10

[0250] -Discharge conditions: CC (~2.2V)-C / 20

[0251] Reference Fig.19 and Fig. 20 The initial capacity of Example 2 is about 181.8 mAh / g, which shows an improved initial capacity compared with the initial capacity of about 174.1 mAh / g of Comparative Example 2. This is considered to be caused by the interface resistance reduction effect of the shell of the alkali metal oxide containing the introduced substitution element.

[0252] Furthermore, it can be seen that after 50 cycles of charge and discharge, Example 2 exhibited a capacity retention rate of about 82.9%, which is superior to Comparative Example 2 which exhibited a capacity retention rate of about 72.5%, and thus had excellent long-term stability and lifespan.

[0253] The embodiments of the present invention are described in detail above. The scope of rights of the present invention is not limited to the above embodiments. Various modifications and improvements made by those skilled in the art using the basic concepts of the present invention defined in the claims are also included in the scope of rights of the present invention.

Claims

1. A composite positive electrode active material for a lithium secondary battery, comprising: a core portion capable of intercalating and deintercalating lithium; and a shell portion, the shell portion covering the surface of the core portion and comprising an alkali metal oxide, in, The alkali metal oxide includes a substituent element that replaces a portion of the alkali metal element and has an oxidation number higher than that of the alkali metal element.

2. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein The substituting element comprises a non-transition metal.

3. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein The alkali metal oxide is represented by the following Chemical Formula 1: [Chemical formula 1] <h2 style=";text-align:left;direction:ltr">(A<h2 style=";text-align:left;direction:ltr"> 1-ax <h2 style=";text-align:left;direction:ltr"> B<h2 style=";text-align:left;direction:ltr"> x <h2 style=";text-align:left;direction:ltr"> )MO3 In the chemical formula 1, the A comprises an alkali metal element, The B comprises at least one selected from magnesium (Mg), aluminum (Al), gallium (Ga), silicon (Si), germanium (Ge), tin (Sn), arsenic (As), antimony (Sb) and combinations thereof, The M comprises at least one selected from niobium (Nb), tantalum (Ta), boron (B), zirconium (Zr), phosphorus (P) and combinations thereof, a is the oxidation number of B, And it satisfies 0.01≤x≤0.

3.

4. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein The alkali metal oxide is represented by the following Chemical Formula 2: [Chemical formula 2] <h2 style=";text-align:left;direction:ltr">[A<h2 style=";text-align:left;direction:ltr"> 1-ax <h2 style=";text-align:left;direction:ltr"> (B1<h2 style=";text-align:left;direction:ltr"> 1-m <h2 style=";text-align:left;direction:ltr"> B2<h2 style=";text-align:left;direction:ltr"> m <h2 style=";text-align:left;direction:ltr"> )<h2 style=";text-align:left;direction:ltr"> x <h2 style=";text-align:left;direction:ltr"> ](M1<h2 style=";text-align:left;direction:ltr"> 1-n <h2 style=";text-align:left;direction:ltr"> M2<h2 style=";text-align:left;direction:ltr"> n <h2 style=";text-align:left;direction:ltr"> O3) In the chemical formula 2, the A comprises an alkali metal element, The B1 and the B2 are different from each other and each independently comprises at least one selected from magnesium (Mg), aluminum (Al), gallium (Ga), silicon (Si), germanium (Ge), tin (Sn), arsenic (As), antimony (Sb), and combinations thereof, The M1 and the M2 are different from each other and each independently comprises at least one selected from niobium (Nb), tantalum (Ta), boron (B), zirconium (Zr), phosphorus (P) and combinations thereof, The oxidation numbers of B1 and B2 are the same, a is the oxidation number of B1 or B2, And it satisfies 0≤m≤1, 0≤n≤1 and 0.01≤x≤0.

3.

5. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein The composite positive active material includes 98 wt % to 99.9 wt % of the core portion and 0.1 wt % to 2 wt % of the shell portion.

6. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein The alkali metal oxide has a trigonal crystal structure and belongs to the R3c space group.

7. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein The alkali metal element and the substituent element occupy the Wyckoff position 6a (0, 0, 0.283).

8. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein The substituent element does not occupy the Wyckoff position 6a (0, 0, 0).

9. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein As the substituting element replaces a portion of the alkali metal element, the lattice volume of the alkali metal oxide decreases compared to when the substituting element is not present.

10. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein As the substituent element replaces a portion of the alkali metal element, the length of the a-axis of the alkali metal oxide obtained by Rietveld analysis of X-ray diffraction decreases compared to when the substituent element is not present.

11. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein As the substituent element replaces a part of the alkali metal element, the length of the c-axis of the alkali metal oxide obtained by Rietveld analysis of X-ray diffraction increases compared to when the substituent element is not present.

12. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein As the substitution element replaces a portion of the alkali metal element, the Bragg angle of at least one (hkl) diffraction peak of the alkali metal oxide among (012), (104), (110) and (113) obtained by Rietveld analysis of X-ray diffraction shifts to a higher angle compared to when the substitution element is not present.

13. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein The shell is a conformal layer.

14. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein As the substituent element replaces a portion of the alkali metal element, the adsorption energy E of the alkali metal oxide to the core portion is increased compared to when the substituent element is not present. ads Increase.

15. The composite positive electrode active material for lithium secondary battery according to claim 1, wherein As the substituting element replaces a portion of the alkali metal element, the activation energy barrier of the alkali metal oxide is lowered compared to when the substituting element is not present.

16. A method for preparing the composite positive electrode active material for a lithium secondary battery according to any one of claims 1 to 15, the method comprising the following steps: preparing a core portion capable of inserting and extracting lithium; preparing a raw material of an alkali metal oxide; adding the core and the raw material into a solvent and stirring to obtain an intermediate material; drying the intermediate material; and The dried intermediate material is heat treated. The composite positive electrode active material for a lithium secondary battery comprises: the core portion; and a shell portion, wherein the shell portion covers the surface of the core portion and comprises an alkali metal oxide. The alkali metal oxide includes a substituent element that replaces a portion of the alkali metal element and has an oxidation number higher than that of the alkali metal element.

17. The method for preparing a composite positive electrode active material for a lithium secondary battery according to claim 16, wherein: The raw material contains alkoxides of respective elements constituting alkali metal oxides.

18. A method for preparing the composite positive electrode active material for a lithium secondary battery according to any one of claims 1 to 15, the method comprising the following steps: preparing a raw material of an alkali metal oxide; The raw material is crushed by a ball mill to obtain a crushed product; heat-treating the pulverized product to obtain an alkali metal oxide; and forming a shell portion including the alkali metal oxide on the surface of the core portion capable of inserting and releasing lithium, The alkali metal oxide contains a substituent element, wherein the substituent element replaces a portion of the alkali metal element and has an oxidation number higher than that of the alkali metal element.

19. The method for preparing a composite positive electrode active material for a lithium secondary battery according to claim 18, wherein: The raw material contains oxides of respective elements constituting alkali metal oxides.

20. A lithium secondary battery comprising: positive electrode; negative electrode; as well as a solid electrolyte layer, the solid electrolyte layer being located between the positive electrode and the negative electrode, The positive electrode comprises the composite positive electrode active material for a lithium secondary battery according to any one of claims 1 to 15.

Images